This invention relates to an improvement in trigger pulse forming circuitry that form trigger pulses synchronized with input pulse signals.
Conventionally, differentiating circuits comprised of resistors and capacitors have been used as trigger pulse forming circuits to trigger monostable multivibrators, etc. However, differentiating circuits have shortcomings in that they do not form a trigger pulse with stable pulse width or amplitude due to the rise and fall time of the input pulse signal and the irregularity of the time constants of the differentiating circuit.
Consequently, a known circuit as shown in FIG. 1 may be used to avoid the foregoing problems, the FIG. 1 circuitry generally corresponding to that disclosed in co-pending application Ser. No. 859,539, filed Dec. 12, 1977, which is incorporated herein by reference. FIG. 1 is a schematic drawing which shows a trigger pulse forming circuit and a pulse shaping circuit that shapes the output of the trigger pulse forming circuit. The trigger pulse forming circuit constitutes an emitter-coupled differential amplifier in which the emitters of transistors 1 and 2 are connected in common and grounded through a constant current source 3. The collector of transistor 1 is connected to the power supply +B.sub.2 through a load resistor 4, the collector of transistor 2 is connected to a power supply +B.sub.1 through an integrating circuit comprising a load resistor 5 and a capacitor 6 and the outputs of transistors 1 and 2 are applied to AND diodes 8 and 9. The pulse shaping circuit comprises a current switching circuit that consists of transistors 10 and 11 and a constant current source 12. The voltage +V.sub.B1 of power supply +B.sub.1 and the voltage +V.sub.B2 of power supply +B.sub.2 are set so that V.sub.B1 &gt;V.sub.B2.
The output pulse of transistor 2 is integrated where the output pulses at the collectors of transistors 1 and 2 are mutually phase-reversed and derived from the input pulse signal impressed on the input terminal IN. The logical product of the above integrated output pulse and the output pulse from transistor 1 is derived from diodes 8 and 9 and used to form the trigger pulse. A shaped trigger pulse is obtained by shaping the waveform with a current switching circuit including transistor 10 and 11. 7 and 15 are power supplies for establishing threshold levels.
When the above-mentioned trigger pulse forming circuit is converted to an integrated circuit, it is desirable to minimize the electrostatic capacitance of capacitor 6 of the integrating circuit. Therefore, as the electrostatic capacitance of capacitor 6 is reduced, the resistance of load resistor 5 must be increased and the current of constant current source 3 reduced. Consequently, the output impedance of the trigger pulse forming circuit increases and the capacity to drive, for example, the pulse shaping circuit, level shifter, or flip-flop circuit in the next stage decreases. In other words, the FIG. 1 circuitry has a shortcoming in that a stable trigger pulse cannot be formed with respect to the irregularities in the values of circuit elements and changes in ambient conditions such as ambient temperature. Thus, there is a problem in converting it to an integrated circuit.